Adjustable magnetic shunt for permanent magnet generators



Sept. 16, 1952 RK 2,610,993

ADJusTABL Patented Sept. 16, 1952 ADJUSTABLE MAGNETIC SHUNT FOR PERMANENT MAGNET GENERATORS Julian H. Stark, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application July 12, 1951, Serial No. 236,311

3 Claims.

This invention relates to dynamoelectric machines and, more particularly, to permanent magnet excited machines having means for preventing demagnetization of the permanent magnets and for adjusting the output voltage.

Many dynamoelectric machines, particularly in the fractional horsepower frame sizes, such as tachometer generators, utilize permanent magnet excitation. In such machines, it is particularly important to provide maximum effective flux density in pole pieces with the minimum amount of permanent material. In conventional machines of this type, having permanent magnet pole pieces, it is customary to first magnetize the stator in a suitable device without the rotor positioned therein, and then to expose the stator to an open air condition of high external reluctance, so that the stator is air stablized prior to assembly of the rotor therein. When the stator is exposed in this manner, the magnet iiux density drops to a fairly low point on the demagnetization curve of the major hysteresis loop in the second quadrant. However, when the rotor is positioned in the stator with an accompanying, greatly-reduced external reluctance, the magnet flux density rises along the minor loop to a predetermined point suiicient to supply the operating flux of the machine. The rotor may thereafter be removed from and replaced in the stator repeatedly without loss of flux, providing however, that it is not subjected to a greater demagnetizing force than that of the original open air reluctance. The minor loop as a result of the air exposure is, however, so low that a relatively large amount of magnet material must be used to produce a given working flux. This condition may bev greatly improved by providing the permanent magnet pole pieces of the stator with a fixed shunt flux path of a somewhat greater reluctance than the reluctance of the working air gap, to carry the magnet iiux when the rotor is not positioned in the stator, and also to protect the permanent magnet pole pieces against demagnetization due to short circuits in the output or the armature and to decrease the effect of air aging. This shunt iiux path is in parallel with the working ux path through the air gap of the machine, and when the rotor is positioned in the stator, bypasses only a small portion of the total ux since the shunt gap reluctance is larger than the Working air gap reluctance between the rotor and the stator. However, as the rotor is not positioned in the stator, the rotor shunt air gap provides a path of comparatively low reluctance so that the flux density does not drop to as low a point on the major hysteresis loop as before, and

the operating range is along a minor hysteresis loop at a considerably higher flux level than would be possible if the shunt flux path were not provided. Thus, the magnetic flux density is held at a higher level when the rotor is removed from or replaced in the stator than would otherwise be the case, and, therefore, more working flux is available from a given amount of permanent magnet material or the size of the permanent magnet pole pieces may be reduced to deliver the required amount oi flux. It has also been found desirable to provide means for conveniently adjusting the output voltage of machines of this type and to accomplish this object by adjusting the amount of iiux bypassed around the working air gap.

It is an object of this invention, therefore, to provide an improved dynamoelectric machine of the permanent magnet excited variety having means for shunting a portion of the flux around the working air gap to prevent demagnetization of the permanent magnets, and for adjusting the output voltage of the machine.

Further objects and advantages of this invention will become apparent and the invention will be better understood by reference to the following description and the accompanying drawings, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

In accordance with this invention, a dynamoelectric machine stator is provided having a shell member with a pair of permanent magnet pole pieces projecting radially inward therefrom. A stationary shunt member formed of a plurality of separate laminations respectively abuts one side of each of the permanent magnet pole pieces and is held in position by leakage ux owing therethrough. This stationary shunt member forms the shunt ux path for preventing demagnetization of the permanent magnet pole pieces. In order to provide for adjustment of the output voltage, an adjustable shunt member formed of a plurality of laminations is provided respectively abutting the other sides of the permanent magnet pole pieces and means are provided for adjusting the amount of engagement of the adjustable shunt member with the other sides of the permanent magnet pole pieces.

In the drawing, Fig. 1 is a view in perspective illustrating the improved construction of this invention showing the adjustable shunt member arranged to shunt the maximum amount of permanent magnet iiux; and Fig. 2 shows the arrangement of Fig. 1 with the adjustable shunt acidosis member arranged to shunt the rninnnum amount oi permanent magnet flux.

Referring now to the drawing, there is shown a stator member l for a dynamoelectric machine having a shell portion 2 formed of magnetic material'and a pair of permanent magnet excited pole pieces 3 and i projecting radially inward therefrom. Each of the pole pieces 3 and d comprises a pair of permanent magnets 5 and 6, and 'l and 8, respectively, with pole shoes d and iii. The pole piece assemblies 3 and l areheld in assembled re1ation by means of suitable screws ii with the permanent magnets being clamped between the pole shoes and tl e yoke. It will be readily understood that any other suitable form of permanent magnet excited pole pieces may .ce utilized in this invention.

In order to provide a shunt ilux path for the permanent magnet pole-piece assemblies and li, a stationary shunt member l2 is provided, f

formedof a plurality of separate laminations i3.

- e-"endportion ifi of the shunt member lirespectively abuts the sides i5 and i@ oi the permanentmagnets 5 and l and the central portion l? is bowed' to accommodatethe armature of the machine (not shown). As will be hereinafter described, it is desirable that the shunt member |2 be saturated with the permanent magnet iiux passing therethrough and, therefore, the number of laminations i3 may be increased or decreased to securethe saturated condition.`

If the permanent magnet pole piece assemblies i-l and tare magnetized with the armature of machine in place, the resultant voltage output will beV higher than required, and it is furthermore desirable to provide means for adjusting theoutput'voltage of the machine. Therefore, an adjustable shunt member iii is provided, formed of a plurality of laminations i9. The adjusta-ble shunt member i8 has its ends i@ and 2l respectively'abutting the sides 22 and 23 of the' permanent magnets 'd and 8, and as shown in Figs, 1 and 2, is movablefrom a rst position as shown in Figi with its end portions 2d and 2-5 respectively abutting'the sides of 22 and 23 of the permanent magnets t and to a second position asv shown in Fig. 2 with its endV portions 24 and v25V completely out of engagement with the sides .22 and'23 of the permanent magnets ii and 8.r Adjustment of the adjustable shunt member I8 is provided by means of a screw 25 seated in thei bowed portion 2i ofthe adjustable Vshunt memberV IS and threadinglg.7 engaging a suitable opening 28 in the shell 2. During assembly, the

magnets 5, 5', 'i and 8 are prevented from circunn ferential movement by the shunts i2 and Thus, by turning the adjusting screw 2S in one direction, the laminations I9 of the adjustable shunt member i8 are moved in against the sides of the permanentmagnets e and 3 so that a larger portion of 4the permanent magnet iiux is shunted around'the armature, thus reducing the output voltage,.and when the screw Z6 is moved in the opposite direction, the laminations are moved away from the permanent magnets ii and B, thus reducing the shunted flux and increasing the'output voltage. Adjustment of the adjustable shunt member 2S by means of the screw 26 will have complete control over the output voltage as long asn the stationary shunt member l2 is saturated.

Without the improved shunt construction described above, thevamount of permanent magnet material required to produce a rated-output voltage ismuch greater because of losses due to air aging, andifurthermore, the possibility of loss of output voltage oi said permanent magnet excitation of the armature or due to removal oi" the armature or overload or short circuit, is eliminated. Furthermore, adjustment of the output voltage is conveniently provided eliminating the necessity for short circuiting a portion of the armature. rWith this arrangement, the eld structure can be magnetized after assembly and positioning of the armature therein without the hasard of excessive demagnetization either by short circuit or removal oi the armature and the user has available a convenient method of calibration or adjustment or" the output voltage.

vWhile have illustrated and described a particular embodiment of this invention, further modihcationsV and improvements will occur to those skilled in the art. I desire that it be understood, therefore, that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scopejof this invention.

What I claim as new and desire to secure by Letters latent of the United States is:

l. In a dynamoeleotric machine, a stator member having a shell member, a pair oi permanent magnet pole nieces projecting radially inward therefrom, a stationary shunt member formed of a plurality of separate lamina-tions respectively abutting one side of each ci said permanent inagnet pole pieces and held in Vposition bylealiage therethrough for preventing demagnetization of said permanent magnet pole pieces, said shunt member being saturated by the leakage hun between said permanent magnet pole pieces,

adjustable shunt member formed of a plural# ity or" laminations respectively abutting the other sides or" said permanent magnet pole pieces, and means for adjusting the amount of engagement of said adjustable shunt member with said permarient magnet pole pi s for controlling the acnine. 2. In a dynamoelectric m chine, a stator member having a shell member, a pair of permanent magnet pole pieces lprojecting radially inward therefrom, a stationary shunt member formed of a plurality of laminations respectively abutting one side or" each of said permanent magnet pole pieces and held in position by leakage iiux therethrough for preventing demagnetization of said permanent magnet pole pieces, said shunt member being saturated by the leakage iiux between Ysaid permanent magnet pole pieces, an adiustable shunt meiber formed of a plurality of laminations having its ends respectively engaging the other sides of said permanent magnet pole pieces and having its end portions adjustably removable from a rst position abutting said other sides of said permanent magnet pole pieces to aV second position with said end portions out of engagement with said other sides of said permanent magnet pole pieces, and means for adjusting the position of said end portions of said adjustable shunt member relative to said other sides u of said permanentmagnet pole pieces for regulating the leakage iiux therethrough whereby the output voltage or" said machine is controlled. In a dynamoelectric machine, a stator member having a shell member, a pair of permanent magnet pole pieces projecting radially inward therefrom, a stationary shunt member formed of a plurality of separate laminations respectively abutting one side of each of said permanent magnet pole pieces and held in position by leakage iiux therethrough for preventing demagnetization of said permanent magnet pole pieces, said shunt member being saturated by the leakage flux between said permanent magnet pole pieces, an adjustable shunt member formed of a plurality of laminations having its ends respectively engaging the other sides of said permanent magnet pole pieces and having its end portions adjustably movable from a rst position abutting said other sides of said permanent magnet pole pieces to a second position with said end portions of engagement with said other sides of said permanent magnet pole pieces, and means for adjusting the position of said end portions of said adjust- REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,720,208 Collins July 9, 19-29 

